1.Alert,vigilant,watchful imply a wide-awake attitude, as of someone keenly aware of his or her surroundings. Alert describes a ready and prompt attentiveness together with a quick intelligence: The tourist was alert and eager to see the sights.Vigilant suggests some immediate necessity for keen, active observation, and for continuing alertness: Knowing the danger, the scout was unceasingly vigilant.Watchful suggests carefulness and preparedness: watchful waiting.

alert

adv.

"on the watch," 1590s, from French alerte "vigilant" (17c.), from phrase à l'erte "on the watch," from Italian all'erta "to the height," from erta "lookout, high tower," noun use of fem. of erto, past participle of ergere "raise up," from Latin erigere "raise" (see erect). The adjective is attested from 1610s, the noun from 1803, and the verb from 1868. Related: Alerted; alerting.